1. Field of the Invention
The present invention relates to an improvement in a liquid-seal type motor in which a rotor section is filled with a lubricating oil and a stator section is filled with an insulating oil.
2. Description of the Prior Art
A conventional liquid-seal type motor will be described with reference to FIG. 1. In FIG. 1, there is shown a cylindrical frame 1. A stator is fixed onto the inner circumferential surface of the frame 1 and a cylindrically formed can 3 is arranged at the inner side of the stator 2. Upper and lower annular end plates 4, 5 are respectively placed at upper and lower ends of and between the can 3 and the frame 1 to be sealingly connected to them. Upper and lower brackets 6, 7 are sealingly connected to the upper and lower end plates 4, 5 respectively. The upper bracket 6 receives in its axial bore an upper bearing 8 to journal the upper part of a rotary shaft 14 on which a rotor 12 is fixed and a communication channel 10 is formed in the axial bore of the upper bracket 6 extending over the entire length of the upper bearing 8. The lower bracket 7 also receives in its axial bore a lower bearing 9 to journal the lower part of the rotary shaft 14 and a communication channel 11 is formed in the axial bore of the lower bracket 7 passing through the same. A shaft sealing device 13 is arranged in the upper bracket 6 to seal the upper end of the rotary shaft 12. The lower bracket 7 is attached at its lower end with a thrust casing 15 which has upper and lower cylindrical parts and an intermediate wall portion 16 at the center of which a through hole 17 is formed. A thrust bearing 18 is supported by the intermediate wall portion 16 to bear a thrust load of the rotary shaft 14. A diaphragm 19 is sealingly fitted to the lower cylindrical recess of the thrust casing 15 to adjust a pressure of lubricating oil filled inside the can 3, the pressure being applied through the communication channel 11 and the through hole 17. A current feeding cable 20 is sealingly connected to the upper bracket 6 to extend to the stator 2.
The cylindrical frame 1, the can 3 and the end plates 4, 5 cooperate to define an insulating oil enclosing part B in which the stator 2 is surrounded by insulating oil, while the can 3, the upper and lower brackets 6, 7 and the rotor 12 cooperate to define a lubricating oil enclosing part A in which the rotor 12 is surrounded by lubricating oil.
In the conventional liquid-seal type motor as described above, when a current is supplied to the stator 2 through the current feeding cable 20, the rotor 12 is rotated to drive a pump (not shown) and so forth connected to the rotary shaft 14 as is well-known.
The operation of the motor causes temperature rise in the stator 2 and the rotor 12 to cause volume expansion of the lubricating oil and the insulating oil contained in the motor. In this case, the frame 1, the can 3 and the upper and lower end plates 4, 5 are jointed by welding at their adjoining parts and accordingly, the insulating oil is certainly enclosed and does not leak outside. On the other hand, the lubricating oil tends to leak out because the rotary shaft 14 passes through the upper bracket 6 even though the shaft sealing device 13 is provided. However, since the diaphragm 19 is sealingly connected to the thrust casing 15, volume expansion of the lubricating oil is absorbed by deformation of the diaphragm 19 through the communication channel 11 and the through hole 17 to thereby prevent pressure rise in the lubricating oil enclosing part A, i.e., increase of a pressure applied to the rotor 12.
When a liquid-seal type motor is used at a high pressure and high temperature, the volume expansion of the lubricating oil and the insulating oil is extremely large. Especially, a pressure in the insulating oil enclosing part B in which the stator 2 is confined becomes high since the insulating oil is completely sealed by the frame 1, and can 3 and the upper and lower end plates 4, 5. As a result, a high pressure is applied to the can 3 formed of a thin plate to thereby cause deformation of the can 3 on the side of the rotor 12. The deformation of the can 3 may cause a serious accident that the can 3 restricts the revolution of the rotor 12 or the joint portions between the upper and lower end plates 4, 5 is broken.